Glacial refugia and postglacial spread of an iconic large European land snail, Helix pomatia (Pulmonata: Helicidae)
Abstract
The Holocene postglacial expansions offer a possibility to assess how quickly snails, with proverbially slow active dispersal and unclear passive dispersal capabilities, can naturally spread. We explore the possibilities and limitations of such an approach on an iconic European snail.
We locate probable sources of postglacial expansion of Helix pomatia and date its earliest postglacial subfossil occurrences in Central Europe, close to presumed natural northern distribution limits. With dense sampling of the species native range, we found most of its mitochondrial diversity at c. 45 degrees N or more southerly.
A hotspot in Bosnia and Serbia contributed to colonization of the Pannonian Basin, Carpathians and Bohemian Massif; however, the most widely distributed lineage has a more westerly centre of diversity, with a possible refugium in Italy. We revised the oldest occurrences post-dating the Late Pleniglacial from Czechia and Slovakia suggested by literature and radiocarbon-dated the preserved shell fragments.
No reliably identified fragment yielded a date earlier than 10 121-9695 cal BP. Stratigraphy-based records presumed older turned out to be unreliable, making the argument for a direct dating approach.
However, our results confirm that in the absence of northern refugia, H. pomatia must have been able to colonize the newly emerging postglacial habitats rapidly.